Pressure sensitive pointing device for transmitting signals to a tablet

Abstract

A pressure sensitive pointing device or pen is described for use with an electronic tablet that determines the position of the pointing device on the surface of the tablet. The pointing device incorporates a variable reluctance circuit responsive to the force exerted on the pen point for modulating a radiating frequency, emanating from the pen, in proportion to the force.

What is claimed is: 
     
       1. A pressure sensitive pen for transmitting signals to a tablet comprising: (a) a stylus mounted within a carrier for limited axial movement and extending therefrom for contact with a surface;   (b) switch means responsive to a first predetermined axial force applied to said stylus for generating a pen down signal; and   (c) modulating means having a variable reluctance responsive to axial forces exceeding a second predetermined axial force larger than said first predetermined axial force for varying said reluctance and for modulating transmitted signals in proportion to said axial forces exceeding said second predetermined axial force.   
     
     
       2. The combination set forth in claim 1 wherein said modulating means comprises an oscillator having a tank circuit and a variable reluctance connected in parallel to said tank circuit for varying the frequency of oscillation. 
     
     
       3. The combination set forth in claim 1 including a first spring biasing means opposing said first predetermined axial force and a second spring biasing means opposing said second predetermined axial force. 
     
     
       4. The combination set forth in claim 3 wherein said modulating means comprises an oscillator having a tank circuit and a variable reluctance connected in parallel to said tank circuit for varying the frequency of oscillation. 
     
     
       5. In a pressure sensitive pen having an oscillator therein for transmitting signals to a receiving tablet, the improvement comprising: (a) a stylus mounted within a carrier for limited axial movement in response to axial forces applied to said stylus;   (b) a ferrite core having a first portion secured to said carrier and a second portion mounted for axial movement with said stylus, said axial movement changing an air gap between said first and second portions; and   (c) a winding in said ferrite core connected in parallel with a tank circuit of said oscillator wherein axial movement of said stylus changes said air gap and modifies the frequency of the signal being transmitted by said pressure sensitive pen.   
     
     
       6. The combination set forth in claim 5 including a spring biasing means for resisting said limited axial movement. 
     
     
       7. The combination set forth in claim 5 wherein said axial movement increases the air gap between said portions of said ferrite core. 
     
     
       8. The combination set forth in claim 6 including a pre-load adjustment means contacting said spring biasing means and adjustably positioned in said carrier for selecting a pre-load force on said spring biasing means. 
     
     
       9. A pressure sensitive pen for transmitting signals to a tablet comprising: (a) a stylus mounted within a carrier for limited axial movement and extending therefrom for contact with a surface;   (b) switch means responsive to axial movement of said stylus for providing a pen down signal;   (c) an actuating rod mounted in said carrier and positioned to receive axial forces from said stylus;   (d) an oscillator mounted in said carrier and having a tank circuit for determining frequency of the signals transmitted by said pressure sensitive pen; and   (e) a variable reluctance means mounted in said carrier connected to said tank circuit and responsive to axial forces received by said actuating rod from said stylus for changing its reluctance in response to changes in said force and to thereby modify the frequency of the signals transmitted by said pressure sensitive pen.   
     
     
       10. The combination set forth in claim 9 wherein said actuating rod is mounted coaxially with said stylus. 
     
     
       11. The combination set forth in claim 9 including a first spring biasing means mounted in said carrier opposing said axial movement of said stylus, and a second spring biasing means mounted in said carrier opposing axial movement of said actuating rod. 
     
     
       12. The combination set forth in claim 11 including a pre-loading adjustment means contacting said second spring biasing means and adjustably positioned in said carrier for selecting a pre-load force on said second spring biasing means. 
     
     
       13. The combination set forth in claim 9 wherein said variable reluctance means comprises a ferrite core having a first portion secured to said carrier and a second portion mounted for axial movement with said stylus, said axial movement changing an air gap between said first and second portions. 
     
     
       14. The combination set forth in claim 9 wherein said variable reluctance means comprises a ferrite core having a first portion secured to said carrier and a second portion mounted for axial movement with said stylus, said axial movement increasing an air gap between said first and second portions, and a winding in said ferrite core connected in parallel with said tank circuit whereby axial movement of said actuating rod reduces said air gap and modifies the frequency of the signal being transmitted by said pressure sensitive pen. 
     
     
       15. The combination set forth in claim 11 wherein said variable reluctance means comprises a ferrite core having a first portion secured to said carrier and a second portion mounted for axial movement with said stylus, said axial movement increasing an air gap between said portions, and a winding in said ferrite core connected in parallel with said tank circuit whereby axial movement of said actuating rod reduces said air gap and modifies the frequency of the signal being transmitted by said pressure sensitive pen. 
     
     
       16. The combination set forth in claim 12 wherein said variable reluctance means comprises a ferrite core having a first portion secured to said carrier and a second portion mounted for axial movement with said stylus, said axial movement increasing an air gap between said portions, and a winding in said ferrite core connected in parallel with said tank circuit whereby axial movement of said actuating rod reduces said air gap and modifies the frequency of the signal being transmitted by said pressure sensitive pen.